Clinical Outcomes of Near-Term Infants

METHODS

Newborn infants who were born between October 1997 and October 2000 (inclusive) were identified using the obstetric electronic medical record database of the Massachusetts General Hospital, a tertiary teaching hospital with 3200 births per year. This secure database contains pertinent information on all mothers and neonates delivered at the Massachusetts General Hospital. Using the medical record number and gestational age of each neonate based on best obstetric estimate, we sorted through 7474 records (593 records of infants of 35–36 6/7 weeks' and 6881 records of infants 37–40 weeks' gestation) and randomly selected 120 near-term (35–36 6/7 weeks' gestation) and 125 full-term (37–40 weeks' gestation) records. To achieve 80% power for a 2-tailed α of .05 with an estimated clinical diagnosis rate of 50% and 30% in near-term and term infant groups, respectively, it was calculated that analysis of 90 near-term and 95 full-term neonatal records were needed.

Exclusion criteria were 1) incomplete medical record, 2) major congenital anomaly, 3) multiple gestation above twins, and 4) maternal substance abuse. This investigation was approved by our institutional review board.

Chart review was performed on each of the randomly selected medical records, and data were entered into a Microsoft Access 97 relational database. Statistical methods incorporated dichotomous variables comparing near-term and full-term infants using Fisher exact test. For significant associations, the maximum likelihood estimate of the conditional odds ratio (OR) and 95% confidence interval (CI) are reported. For nondichotomous categorical variables (eg, management of possible sepsis), Fisher exact test for an R × C table is used. For ordinal variables (eg, length of stay, Apgar scores), the Wilcoxon rank sum test was used for comparison of medians. The R statistical package (version 1.5.0) was used for statistical computations.⁶

Cost and charge information was obtained through the Eclipsys Sunrise Decision Support Manager (previously Transition Systems, Inc). Patient unit numbers were used to identify patient admissions in the system. When multiple admissions existed for the same patient, admit dates were evaluated to distinguish the newborn admission from subsequent admissions, which were excluded. Reports were then generated to capture each patient's direct costs and actual total cost (including overhead), which were then summarized and analyzed by gestational age categories. All information obtained from the Eclipsys SDSM system reflected hospital-based activity only. The physician component of expense was not included.

RESULTS

Ninety near-term and 95 full-term infants of the 120 near-term and 125 full-term infant records selected for enrollment met inclusion criteria and avoided exclusion criteria for data collection and analysis. All medical records selected for enrollment were available to review. Medical records of 29 full-term infants and 19 near-term infants were incomplete and excluded from analysis.

Median lengths of hospital stay for near-term and full-term infants were comparable; however, wide variations in hospital stay were documented for near-term infants after both vaginal (P = .03, Wilcoxon rank sum) and cesarean (P = .003, Wilcoxon rank sum) deliveries (Table 1, Fig 1). The mean birth weight (±standard deviation) of near-term and full-term infants was 2638 ± 436.6 g and 3294 ± 497.2 g, respectively. Median Apgar scores at 1 and 5 minutes were 8 and 9, respectively, for both near-term and full-term infants; Apgar scores were also concordant between quartiles (Table 2). No study patient had an Apgar score at 5 minutes assigned <3.

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Fig 1.

Scatterplot of neonatal gestational age versus length of hospital stay. Near-term infants are represented by black diamonds, and full-term infants are represented by gray dots. The scatterplot displays 1 value for each unique intersection of infant gestational age and length of stay. However, if 4 patients of 36.7 weeks of gestation have newborn hospital stays of 2 days, then only 1 plot point is graphed to represent all 4 cases.

Nearly all analyzed clinical outcomes differed between near-term and full-term neonates (Fig 2). Near-term newborns were more likely than full-term newborns to exhibit temperature instability (10% vs 0%; OR: infinite; P = .0012, Fisher exact test [FE]) or hypoglycemia (15.6% vs 5.3%; OR: 3.30; 95% CI: 1.1–12.2; P = .028, FE). Near-term infants received intravenous infusions more often (26.7% vs 5.3%; OR: 6.48; 95% CI: 2.27–22.91; P = .0007, FE). The near-term infants had respiratory distress much more often than the term newborns (28.9% vs 4.2%; OR: 9.14; 95% CI: 2.9–37.8; P < .00001, FE) and were clinically jaundiced more often (54.4% vs 37.9%; OR: 1.95; 95% CI: 1.04–3.67; P = .027, FE). Apnea and bradycardia were seen infrequently and only in the near-term group; this difference was insignificant (4.4% vs 0%; P = .054, FE).

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Fig 2.

Graph of clinical outcomes in near-term and full-term infants as percentage of patients studied. Near-term newborn data are graphed with gray bars, full-term data with black bars.

Near-term infants were much more likely than full-term infants to have a clinical problem resulting in the assignment of 1 or more diagnoses (77.8% vs 45.3%; OR: 4.20; 95% CI: 2.14–8.49; P < .0001, FE). Near-term infants were twice as likely to have several clinical problems resulting in the assignment of 2 or more diagnoses (50% vs 21.1%; OR: 3.72; 95% CI: 1.88–7.55; P < .0001, FE). Additional analysis showed that 18 of the 95 near-term infants had 6 or more diagnoses compared with 0 of 90 term infants.

Near-term infants underwent sepsis evaluations more frequently than full-term infants (36.7% vs 12.6%; OR: 3.97; 95% CI: 1.82–9.21; P = .00015, FE). For those who underwent sepsis evaluations, we compared clinical assessment and treatment approaches (Table 3). Although more near-term infants received 7-day antibiotic courses, differences in clinical management of possible sepsis did not reach statistical significance.

Near-term infants with diagnoses of clinically apparent jaundice or poor feeding were more likely to have a delay in discharge beyond 48 hours of hospitalization after vaginal delivery and beyond 96 hours after cesarean delivery (Table 4). Fifty near-term infants compared with 7 term infants had a delayed discharge home. Seventy-six percent of near-term infants with poor feeding experienced a delay in discharge to home, whereas 28.6% of term infants with poor feeding had delayed discharge (95% CI: 0.94–93.4; OR: 7.3; P = .029, FE).

Total and direct costs were calculated and analyzed for each study patient. Cost analyses revealed that the relative increase in total costs for near-term compared with term infants was 2.93 (mean) and 1.39 (median), resulting in a cost increase of $2630 (mean) and $429 (median; P = .0004, Wilcoxon rank sum test). The relative increase in direct costs for near-term infants was 2.89 (mean) and 1.32 (median), resulting in a cost difference of $1596 (mean) and $221 (median) per patient (P = .0003, Wilcoxon rank sum test).

DISCUSSION

Important differences in clinical outcomes became apparent when the hospital courses of near-term infants were compared with those of full-term infants. Despite appropriate size and favorable Apgar scores, near-term infants had significantly more documented medical problems when compared with contemporaneous full-term neonates. This resulted in increased health care costs in the group born near to term. Near-term newborns, in this retrospective analysis, were observed to exhibit certain clinical problems associated with prematurity. In clinical nursery settings, we have the experience that near-term infants “masquerade” as term infants on the basis of their relatively large size and mature, chubby appearance. Although progressive developmental immaturity is expected with very low birth weight and extremely low birth weight infants, this may not be the clinical expectation for near-term infants, despite the recognized direct relationship between gestational age and maturation.

Nearly 30% of near-term infants in our study had clinical evidence of respiratory distress, and one third of those were delayed in their discharge to home because of it. Of these near-term infants with respiratory signs, 10% were treated with a 7-day course for presumptive pneumonia. There is clinical overlap among pneumonia, transient tachypnea of the newborn (TTN), and (mild) respiratory distress syndrome, making it difficult at times to distinguish the cause of neonatal respiratory symptoms. Amniotic fluid lecithin/sphingomyelin ratios typically suggest fetal lung maturity for fetuses of 35 weeks of gestation and above. Using a conservative criterion for lung maturity, ≥3% phosphatidylglycerol content, 30% to 65% of infants in the near-term gestational range would be predicted to have biochemically mature lungs.⁹ Although respiratory distress was noted to be a frequent problem in near-term infants, this analysis did not address cause. Lung immaturity should be one consideration in the differential diagnosis along with meconium aspiration, TTN, and pneumonia in these settings.

Temperature instability was a common clinical problem observed in the near-term infants. Given their relatively large size with average birth weights of >2.6 kg, when compared with very low birth infants and their risk for thermal instability,¹⁰ the number (10%) requiring active temperature management was interesting. Temperature instability may be a presenting sign of neonatal sepsis. Although documented sepsis was not seen more often in near-term infants, this data set is of insufficient size to exclude an increased incidence of sepsis, given that prematurity is a recognized risk factor for neonatal sepsis.¹¹ Obtaining blood cultures followed by short-course antibiotic treatment (pending culture results) may be a reasonable management strategy in the setting of hypothermia and delivery before term (without maternal indications), especially when additional risk factors are present.

That Apgar scores measured in near-term and full-term infants were similar was not an unexpected finding. In addition to documenting physiologic responses, Apgar scores are related to maturity. However, infants of 35 to 36 6/7 weeks' gestation generally are not expected to have the lower Apgar scores measured in more premature infants.¹² A component of perinatal depression in certain study infants cannot be ruled out, though, because additional information, such as umbilical cord blood gas data, is not available.

Low blood sugar was found 3 times as often in our near-term cohort. Of infants with blood glucose values <40 mg/dL, nearly two thirds in each group required treatment with intravenous dextrose, whereas the remaining were able to resolve initial hypoglycemia with early feedings. Premature infants are at risk for hypoglycemia because of low total body fuel stores, inadequate dietary intake, and a tendency to be affected by other conditions, such as cold stress or sepsis, known to contribute to hypoglycemia.¹³ The well-infant clinician must be alert to the potential for neonatal hypoglycemia and have an appropriately low threshold, particularly in near-term infants, for measuring blood sugar and treating as needed.

Twenty-seven percent of all near-term infants studied had a clinical condition whereby intravenous fluid was given compared with only 5% of all term infants. A variety of clinical problems, including hypoglycemia and poor feeding, precipitated this treatment, which is a relatively labor-intensive procedure in the well-infant nursery.

Jaundice is a frequent clinical issue in the newborn period with infrequent but potentially tragic complications. The 54% frequency of clinically appreciated jaundice in our near-term infants differed from that observed in the term infants (37.9%). More notable, though, was that 1 term infant had a delayed discharge as a result of assessment and treatment of jaundice compared with 8 in the near-term group. Maisels and Kring¹⁴ reported that infants who are discharged from the well-infant nursery of ≤38 weeks' gestation have an OR of >7 of being readmitted to the hospital with hyperbilirubinemia. The Pilot Kernicterus Registry, established in 1992 to collect data on term and near-term neonates who receive a diagnosis of kernicterus, identified 90 affected term and near- term infants by 2001.⁵ Near-term newborns are prone to developing hyperbilirubinemia and its sequelae and to require hospital readmission for treatment. Thus, careful observation and slightly longer initial hospital courses in some cases may be indicated.

We found that near-term infants were evaluated for possible sepsis ∼3 times as often as full-term infants. The majority of evaluated near-term infants received antibiotic treatment. Term infants tended to have blood work drawn but were not started on antibiotics. Thirty percent of evaluated near-term infants were treated with antibiotics for 7 days, and pneumonia was the most frequent diagnosis. None of the infants who were treated with antibiotics in either group had a positive blood culture, but this data set is not large enough to draw conclusions about sepsis attack rates. This presents a dilemma for the clinician. Near-term study infants, often observed with (nonsevere) respiratory findings, had sterile cultures; mild respiratory distress syndrome and TTN were possible causes, but respiratory infection would seem less likely when short hospital stays were seldom prolonged for respiratory reasons. Clinical practice dictates that near-term infants be treated as term infants with respiratory signs; thus, clinicians may tend to manage such respiratory distress conservatively as potential bacterial pneumonia.

The near-term infants studied clearly had more clinical problems than term infants and were also likely to be delayed in discharge to home because of these problems. Feeding problems were the dominant reason for a delay in discharge. Given that immature infants are less able to achieve effective sucking and swallowing, this was not entirely unexpected. In our clinical experience, many near-term infants require repeated assistance and support before achieving consistent, nutritive breastfeeding. Supplementation with expressed breast milk or formula, at least initially, is often required.

We found that near-term infants were more likely to have at least 1 medical problem and also more likely to have 2 or more diagnoses assigned when compared with term infants. The developmentally less mature infants exhibited more variability in health status, particularly highlighted in the cluster of 18 near-term infants with 6 documented medical diagnoses.

One study limitation is our inability to define objectively breastfeeding success and to analyze adequately breastfeeding status at time of discharge. Successful breastfeeding is an important component of newborn discharge criteria. Discharge to home for near-term infants was delayed by suboptimal feeding in nearly one fourth of all near-term infant cases. Breastfeeding at discharge of mother and infant from our well-infant nurseries approaches 80% (K.S. Nash, personal communication); thus, breastfeeding status certainly plays a role in discharge timing. In clinical practice, we pay careful attention to potential failed breastfeeding, to prevent early dehydration, additional breastfeeding problems, and hospital readmission.

Length of stay was not increased for near-term infants who were born via the vaginal route or by cesarean section, despite increased variability compared with full-term infants. However, cost of hospitalization for near-term infants was significantly greater, again, with wide variation in data for near-term infants. Length of hospitalization and neonatal diagnosis related groups predict part of the cost of newborn care, and there exists a recognized inverse correlation between birth weight and hospital costs.¹⁵ This helps to explain the discrepancy between the median lengths of stay (which were similar) and the larger number of near-term infants with a delay in discharge. In a recent analysis of larger premature infants (34, 35, and 36 weeks of gestation), nursery-related costs and risk of respiratory distress significantly decreased with each week gained beyond 34 weeks.¹⁶

This study does not address whether the clinical outcomes studied have long-term implications. The next step will be follow-up of near-term newborns with particular emphasis on hospital readmission, frequency of pediatric visits, and feeding success (together with growth). Our aim in this study was to explore whether near-term infants had more clinical problems and longer hospital stays generating greater costs. Given that delivery decisions are driven by both maternal and fetal indications, in settings where near-term delivery is contemplated but nonurgent, these data detailing clinical problems encountered in near-term infants may be instructive.